1. Field of the Invention
This invention relates to the manufacture of uniform glass fiber mats by the wet-laid process, and more particularly, it is concerned with improved glass fiber dispersion compositions for use in such a process.
2. Description of the Prior Art
High strength, uniform, thin sheets or mats of glass fibers are finding increasing application in the building materials industry, as for example, in asphalt roofing shingles and as backing sheets for vinyl flooring. These glass fiber mats are replacing similar sheets made traditionally of asbestos fibers. Glass fiber mats usually are made commercially by a wet-laid process, which is carried out on modified paper making machinery, as described, for example, in the book O. A. Battista, Synthetic Fibers in Papermaking (Wiley) N.Y. 1964. A number of U.S. patents also provide a rather complete description of a wet-laid process, including U.S. Pat. Nos. 2,906,660; 3,012,929; 3,021,255; 3,050,427; 3,103,461; 3,108,891; 3,228,825; 3,634,054; 3,749,638; 3,760,458; 3,766,003; 3,838,995; 3,905,067; 4,179,331 and 4,810,579. The German OLS No. 2454354 (Fr. Demande No. 2,250,719), June, 1975, also is pertinent art in this field.
In general, the known wet-laid process for making glass fiber mats comprises first forming an aqueous suspension of short-length glass fibers under agitation in a mixing tank, then feeding the suspension through a moving screen on which the fibers enmesh themselves while the water is separated therefrom. However, unlike natural fibers, such as cellulose or asbestos, glass fibers do not disperse well in water. Actually, when glass fibers, which come as strands or bundles of parallel fibers, are put into water and stirred, they do not form a well-dispersed system. In fact, upon extended agitation, the fibers agglomerate as large clumps which are very difficult to redisperse.
In an attempt to overcome this inherent problem with glass fibers, it has been the practice in the industry to provide suspending or dispersing aids for the glass fibers, including surfactants, in order to keep the fibers separated from one another in a relatively dispersed state. Such suspending aids usually are materials which increase the viscosity of the medium so that the fibers can suspend themselves in the medium. Some suspending aids actually are surfactants which function by reducing the surface attraction between the fibers. Fatty amine ethoxylates (FAE), amine oxide, nonionic and cationic surfactants are some materials that have been used in the manufacture of non-woven glass fiber mats. However, not all of the available suspending aids are entirely satisfactory for large volume manufacture of useful, uniform glass fiber mats.
For example, such polymeric suspending aids materials as polyacrylamides, hydroxyethyl cellulose and the like, provide a highly viscous aqueous solutions at high material concentrations, but which is difficult to handle, and particularly, which drains very slowly through the mat forming screen, or foraminous belt. Furthermore, the degree of the suspension formed using such materials is only fair, and suspensions having a fiber consistency of more than 0.005% give poor quality mats. The viscous suspensions also trap air upon agitation near the formation zone to form stable foams which adversely affect the uniformity and strength of the mats. Finally, the polymers are not effective at low concentrations, and so are expensive for use in what should be a low cost process.
A number of surfactant materials have been tried for dispersing glass fibers in water, for example, the cationic nitrogen surfactants described in Ger. DT No. 2454354/Fr. Demande No. 2,250,719 (June, 1975). With these surfactants, the glass fiber filaments are drawn from an extruder nozzle, coated with the cationic surfactant, and moistened before chopping into short-length fibers. The chopped fibers then are compounded in another aqueous solution of a cationic surfactant. Accordingly, in this process, the cationic surfactants are applied in two stages to form the desired aqueous dispersion. Furthermore, the quality of the dispersions using the materials of this patent application also is poor. U.S. Pat. No. 4,179,331 shows the use of amine oxides surfactants and Japanese patent applications Nos. 91-44398 and 85-158300 show the use of betaine surfactants as dispersants.
It is also known that surfactants can present foaming problems which can result in bubbles in the final product. A surfactant can be used to the extent that it causes foaming problems or to the extent that a defoamer can alleviate the problem. In the former case, this can limit the effectiveness of any particular surfactant. Since the process of making the dispersions can vary, and the rate of foaming can vary, the acceptable levels of surfactant can vary. The use of defoamers, while effective in many cases, but they are not used extensively as they can add extensive costs and make the process uneconomical. While fatty amine ethoxylates are standard dispersants for use in glass fiber matting, these materials can act as foam stabilizers which means for more foam can be observed when used in the presence of soluble extractives from the sizing carried on the fiber.
It is also common to size fibers, the basic functions of a well-designed sizing being: 1) as a lubricant--coolant in the glass forming process and through the chopper to keep the mass of fibers dense; 2) as a moist binding agent to provide 14%-16% water pickup for the 800 to 2,000 filaments per bundle (about 1.5% of the water is size solids, which equals 2,500 ppm size add-on to the glass; 3) as a dispersion aid in the pulper--the carry through of hydrophilic polymers and surfactants will enable the initial breakup of the bundles to occur which adds many of the unknown variables to the white water and 4) as a silane coupling agent for resins.
The dwell time of the fibers in the slusher is critical for the sizing to be fully effective. Downtime and upsets, especially over 45 minutes, can cause extensive leaching of the sizing chemicals into the white water. Subsequent operation of the slusher can show very erratic demand for both dispersant and thickener polymer.
Therefore, it is apparent that for a glass fiber dispersion technique to be effective, it is necessary that the dispersions meet several rigid criteria simultaneously which can provide means for making the desired high quality, uniform glass fiber mats at a rapid rate of production in an economically acceptable process. Such criteria are listed below:
1. The dispersing surfactant should provide a uniform dispersion of glass fibers in water effectively at low surfactant concentrations. PA1 2. The dispersions should be efficient at high glass fiber consistencies so that the mats may be formed without having to expend an unnecessarily large amount of energy to separate and handle large quantities of water. PA1 3. The dispersion compositions preferably should not be accompanied by a substantial increase in the viscosity of the medium, which would necessitate extensive pumping equipment at the screen to separate the fibers from the water, and which would make drying of the wet mat difficult. PA1 4. The dispersion compositions should be capable of producing glass fiber mats which have a uniform distribution of fibers characterized by a multidirectional array of fibers. The finished mat product should possess uniform high-strength properties, particularly good tensile strength. PA1 5. The dispersions should be capable of use in the wet-laid process in conventional equipment, at high rates of mat production, without generation of unwanted foams, and without corroding the plant machinery. PA1 6. The surfactant materials preferably should be readily available, at low cost, and be capable of use either by direct addition to the fibers in water, or by precoating the fibers with the surfactant before admixing with water to form the aqueous dispersion composition. PA1 7. The surfactant materials preferably should be capable of dispersing unsized as well as sized glass fibers.
These and other objects and features of the invention will be made apparent from the following more particular description of the invention.